Autism Spectrum Disorder (ASD) is a common neurocognitive defect found in children. Patients with Smith-Lemli-Opitz syndrome (SLOS) have a defect in cholesterol synthesis. The majority of patients with SLOS have autistic symptoms. We thus evaluated a cohort of ASD patients for SLOS. Although no SLOS patients were identified, a higher than expected number of children with ASD had hypocholesterolemia. Our goal is to see if we can use cholesterol levels to define an endophenotype of ASD to identify the genetic cause of ASD in a subset of ASD patients. This will be done by exome/genome sequencing. We also have initiated a clinical trial to determine if ASD patients with low cholesterol will respond to dietary cholesterol supplementation.